NWGAA Field
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NWGAA Field clear sky chart from 2005-11-05 to 2017-10-06.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
47%
15481
23%
47159
16%
15438
55%
15438
28%
29213

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
26%
720
22%
2327
10%
716
41%
716
20%
1501
January16th to endNight
26%
768
24%
2421
12%
768
40%
768
22%
1586
February1st to 15thNight
27%
704
24%
2112
9%
701
41%
701
26%
1304
February16th to endNight
24%
631
22%
1893
9%
631
36%
631
22%
1230
March1st to 15thNight
29%
720
22%
2097
12%
720
38%
720
24%
1361
March16th to endNight
37%
768
21%
2112
13%
768
43%
768
28%
1357
April1st to 15thNight
41%
578
25%
1836
15%
578
53%
578
33%
1037
April16th to endNight
46%
540
26%
1730
18%
540
55%
540
32%
988
May1st to 15thNight
49%
540
20%
1620
12%
540
57%
540
29%
1000
May16th to endNight
64%
561
21%
1682
15%
561
68%
561
33%
1000
June1st to 15thNight
72%
540
17%
1620
14%
540
74%
540
33%
996
June16th to endNight
78%
540
18%
1620
15%
540
79%
540
36%
941
July1st to 15thNight
72%
510
14%
1530
12%
510
73%
510
28%
977
July16th to endNight
71%
564
17%
1595
16%
531
72%
531
29%
1017
August1st to 15thNight
74%
539
20%
1680
21%
536
75%
536
30%
1043
August16th to endNight
67%
573
19%
1910
20%
573
69%
573
24%
1256
September1st to 15thNight
62%
672
17%
1932
16%
672
63%
672
26%
1297
September16th to endNight
62%
717
27%
1980
21%
717
66%
717
35%
1208
October1st to 15thNight
56%
684
33%
1881
25%
684
63%
684
39%
1089
October16th to endNight
49%
704
32%
2129
25%
704
59%
704
34%
1214
November1st to 15thNight
48%
700
29%
2276
23%
700
60%
700
34%
1239
November16th to endNight
38%
720
27%
2340
18%
720
51%
720
27%
1368
December1st to 15thNight
31%
720
22%
2340
13%
720
43%
720
22%
1502
December16th to endNight
28%
768
19%
2496
13%
768
37%
768
18%
1702

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
13%5%25%5%35%5%5%7%40%
48035
Night
12%42442445%7%45%
47358
TransparencyDay
41%6%11%19%16%4
47736
Night
37%5%11%20%19%5%
47161
SeeingDay
15%7%20%23%21%12%
5370
Night
15%7%23%28%21%3
15483

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
19%7%24433345%41%
1611
16th to endDay
17%6%25%32344444%
1801
February1st to 15thDay
18%8%24323446%41%
1750
16th to endDay
18%6%35%5%23345%41%
1580
March1st to 15thDay
18%6%26%43435%6%39%
1863
16th to endDay
15%6%35%43445%7%40%
2111
April1st to 15thDay
12%6%25%5%35%446%44%
2121
16th to endDay
11%5%25%5%345%46%44%
2229
May1st to 15thDay
12%6%345%35%447%42%
2331
16th to endDay
9%425%5%36%6%6%9%39%
2431
June1st to 15thDay
7%5%26%6%47%6%7%10%35%
2340
16th to endDay
6%325%5%45%7%8%11%40%
2340
July1st to 15thDay
10%5%25%6%46%6%7%11%31%
2340
16th to endDay
6%436%7%5%9%9%7%10%28%
2465
August1st to 15thDay
7%425%6%47%8%9%11%32%
2266
16th to endDay
12%5%36%8%5%7%6%7%8%28%
2292
September1st to 15thDay
12%6%26%6%45%6%6%8%34%
2016
16th to endDay
14%424434447%45%
1980
October1st to 15thDay
11%42442334455%
1877
16th to endDay
13%5%2432223357%
1741
November1st to 15thDay
13%423313245%54%
1582
16th to endDay
18%414323246%48%
1620
December1st to 15thDay
19%6%35%424446%39%
1620
16th to endDay
25%8%25%5%2234435%
1728
January1st to 15thNight
19%5%2442435%5%41%
2327
16th to endNight
17%6%35%424435%42%
2421
February1st to 15thNight
15%5%25%424335%47%
2103
16th to endNight
18%5%3433435%5%42%
1893
March1st to 15thNight
15%6%245%25%45%6%42%
2097
16th to endNight
12%5%35%5%24346%46%
2112
April1st to 15thNight
12%423313448%51%
1836
16th to endNight
9%42333345%6%52%
1730
May1st to 15thNight
10%4245%3445%7%47%
1619
16th to endNight
7%424425%6%6%10%46%
1682
June1st to 15thNight
5%3145%36%6%7%12%43%
1620
16th to endNight
32145%35%5%7%13%46%
1620
July1st to 15thNight
6%4245%48%7%7%11%38%
1620
16th to endNight
4336%5%37%5%8%12%38%
1703
August1st to 15thNight
5%315%5%36%5%8%11%42%
1691
16th to endNight
11%426%5%25%6%7%9%38%
1910
September1st to 15thNight
10%426%6%345%6%9%39%
1932
16th to endNight
11%414424447%49%
1980
October1st to 15thNight
10%414323236%57%
1881
16th to endNight
10%42442223358%
2129
November1st to 15thNight
13%313323336%56%
2276
16th to endNight
15%5%23323345%49%
2340
December1st to 15thNight
17%6%345%23446%41%
2340
16th to endNight
23%7%24424346%35%
2496

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
45%47%17%21%3
1612
16th to endDay
42%37%20%19%5%
1801
February1st to 15thDay
43%48%21%19%2
1752
16th to endDay
46%36%19%20%3
1580
March1st to 15thDay
45%5%8%16%19%4
1863
16th to endDay
43%5%13%21%14%2
2112
April1st to 15thDay
40%5%9%20%19%5%
2121
16th to endDay
38%5%8%22%18%5%
2229
May1st to 15thDay
40%5%12%21%15%3
2331
16th to endDay
38%9%14%20%13%3
2435
June1st to 15thDay
39%10%17%21%9%1
2340
16th to endDay
34%8%17%22%14%3
2340
July1st to 15thDay
42%9%19%17%8%2
2201
16th to endDay
41%13%18%15%8%1
2310
August1st to 15thDay
37%12%17%20%9%2
2253
16th to endDay
48%11%13%14%10%2
2292
September1st to 15thDay
44%9%13%15%11%4
2016
16th to endDay
38%6%10%19%20%4
1980
October1st to 15thDay
31%5%7%18%27%8%
1877
16th to endDay
33%25%18%29%9%
1741
November1st to 15thDay
33%35%17%32%7%
1582
16th to endDay
38%37%17%26%6%
1620
December1st to 15thDay
45%48%19%17%4
1620
16th to endDay
52%37%17%14%3
1728
January1st to 15thNight
43%48%18%21%4
2327
16th to endNight
44%45%20%20%5%
2421
February1st to 15thNight
39%28%21%20%6%
2112
16th to endNight
43%36%22%20%3
1893
March1st to 15thNight
41%5%8%20%17%7%
2097
16th to endNight
39%410%26%17%2
2112
April1st to 15thNight
32%411%24%22%6%
1836
16th to endNight
32%410%24%20%6%
1730
May1st to 15thNight
36%7%14%19%20%2
1620
16th to endNight
30%9%17%24%15%2
1684
June1st to 15thNight
30%9%20%24%12%1
1620
16th to endNight
26%9%19%22%17%3
1620
July1st to 15thNight
33%11%18%21%11%2
1530
16th to endNight
34%10%19%20%11%2
1595
August1st to 15thNight
33%9%17%21%14%2
1680
16th to endNight
38%10%16%17%13%2
1910
September1st to 15thNight
39%9%16%16%13%4
1932
16th to endNight
33%5%11%24%20%5%
1980
October1st to 15thNight
29%48%21%25%9%
1881
16th to endNight
32%3416%31%12%
2129
November1st to 15thNight
30%27%18%28%12%
2276
16th to endNight
36%36%18%26%7%
2340
December1st to 15thNight
43%49%18%19%4
2340
16th to endNight
50%39%17%16%3
2496

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
26%20%30%18%22
90
16th to endDay
17%30%43%6%2
96
February1st to 15thDay
21%27%42%6%2
90
16th to endDay
29%14%41%13%
81
March1st to 15thDay
24%20%28%22%31
153
16th to endDay
19%12%32%23%11%
288
April1st to 15thDay
20%11%30%16%19%1
270
16th to endDay
13%5%27%28%20%4
270
May1st to 15thDay
14%10%27%20%12%14%
288
16th to endDay
15%219%25%22%14%
331
June1st to 15thDay
11%112%23%26%24%
315
16th to endDay
10%113%26%22%25%
315
July1st to 15thDay
10%13%25%24%25%
305
16th to endDay
9%17%18%37%26%
326
August1st to 15thDay
13%110%27%29%17%
313
16th to endDay
15%18%24%31%18%
332
September1st to 15thDay
13%312%23%29%17%
315
16th to endDay
13%313%28%30%10%
314
October1st to 15thDay
13%6%18%31%24%6%
278
16th to endDay
15%6%23%22%26%4
234
November1st to 15thDay
23%15%24%22%13%1
90
16th to endDay
20%11%41%14%11%2
90
December1st to 15thDay
24%22%31%18%21
90
16th to endDay
37%16%26%17%2
96
January1st to 15thNight
24%14%30%23%7%
720
16th to endNight
22%14%33%26%3
768
February1st to 15thNight
19%14%35%27%2
704
16th to endNight
20%17%36%22%3
631
March1st to 15thNight
18%14%34%26%6%
720
16th to endNight
15%12%29%29%12%
768
April1st to 15thNight
14%10%31%28%14%
578
16th to endNight
11%7%30%31%17%
540
May1st to 15thNight
10%5%27%29%24%2
540
16th to endNight
10%215%34%32%5%
563
June1st to 15thNight
7%111%32%38%8%
540
16th to endNight
418%31%42%11%
540
July1st to 15thNight
9%8%27%42%12%
510
16th to endNight
6%10%21%46%13%
564
August1st to 15thNight
6%9%29%42%10%
539
16th to endNight
12%16%28%42%7%
573
September1st to 15thNight
13%29%28%38%6%
672
16th to endNight
14%114%33%34%2
717
October1st to 15thNight
13%321%34%23%3
684
16th to endNight
11%8%24%31%21%2
704
November1st to 15thNight
14%7%25%30%19%2
700
16th to endNight
18%12%27%29%12%
720
December1st to 15thNight
21%13%29%26%8%
720
16th to endNight
27%11%29%24%6%
768
Page generated at 2017-10-07 14:07:57. Version ac04

Copyright 2017 A. Danko


NWGAA Field Clear Sky Chart | Charts Home